1. Field of the Invention
The present invention relates to carburization treatment methods for carburizing steel material and a carburization treatment apparatus suitable for carrying out the carburization treatment methods.
2. Description of the Related Art
Various methods are known for carburizing steel material, such as a gas carburization method, a vacuum carburization method, and a plasma carburization method, with each having both advantages and disadvantages.
However, one gas carburization method has a disadvantage of the generation of a large amount of CO2 gas and a possibility of an explosion. A further problem associated with this method is that intergranular oxidation will occur on the surface of the steel material. On the other hand, another gas carburization method using an endothermic gas makes it necessary to employ a metamorphism furnace, hence suffering from a problem of high equipment cost.
A vacuum carburization method is associated with a problem in that once the carbon concentration on the surface of a steel material is increased to a predetermined solid solubility, a large amount of soot will be undesirably generated. As a result, not only does the carburization equipment need a comparatively long time and a considerably high cost for maintenance, but also such equipment does not have sufficient versatility. Moreover, another problem associated with this method is that it is difficult to perform a carbon potential control in an atmosphere within the furnace, if compared with the above-described gas carburization methods. In addition, a plasma carburization method is said to be low in productivity.